Industry has found many uses for the hydrodynamically lubricated, ring shaped squeeze packing type rotary shaft seals embodying the principles set forth in U.S. Pat. Nos. 4,610,319 and 5,230,520 and marketed by Kalsi Engineering, Inc. of Sugar Land, Tex. under the registered trademark, Kalsi Seals.RTM.. Kalsi Seals are used to provide lubricant retention and contaminant exclusion in harsh abrasive environments, such as the downhole oil field drilling environment. Present commercial oil field applications include rotary cone rock bits, mud motors, high speed coring swivels, and rotating drilling heads. All references herein to hydrodynamically lubricated seals or hydrodynamic seals are directed to seals embodying the principles of the above identified U.S. Patents.
FIGS. 1, 2, 2A and 3 of this specification represent Kalsi Seals prior art which is discussed herein to enhance the readers' understanding of the distinction between the prior art seals and the present invention.
Referring now to the prior art of FIG. 1 there is shown a cross-sectional view of a hydrodynamically lubricated squeeze packing type rotary shaft sealing assembly generally at 1 including a housing 2 from which extends a rotary shaft 3. The housing defines an internal seal installation groove, seat or gland 4 within which is located a ring shaped hydrodynamic rotary shaft seal 5 which is constructed in accordance with the principles of the above mentioned patents and which is shown in greater detail in the partial sectional views of FIGS. 2 and 2A.
FIG. 2 represents the cross-sectional configuration of the prior art seal 5 when located within its seal groove and radially compressed between the rotary shaft and the radially outer wall of the seal groove, and FIG. 2A represents the radially uncompressed cross-sectional shape of the prior art seal.
The hydrodynamic seal is used to separate the lubricant 6 from the environment 7, and to prevent intermixing of the lubricant and the contaminant matter present within the environment. The environment usually contains highly abrasive particulate matter within a liquid vehicle; an example of such an environment would be oil field drilling fluid. From an overall orientation standpoint, the end of the seal which is oriented toward the lubricant is surface 8 and the end of the seal which is oriented toward the environment 7 is surface 9.
When the seal 5 is installed in the circular seal groove or seat 4, a circular radially protruding static sealing lip 10 is compressed against a counter-surface 11 of the groove per the teachings of U.S. Pat. No. 5,230,520. At the inner periphery of the circular sealing element 5 there is provided an inner circumferential sealing lip 12 that defines a dynamic sealing surface 13 that is compressed against a counter-surface 14 of the rotatable shaft 3. The circular seat or seal groove 4 is sized to hold the resilient circular sealing element 5 in radial compression against the cylindrical sealing surface 14 of the shaft 3, thereby initiating a static seal with the housing and shaft in the same manner as any conventional squeeze packing seal, such as an O-Ring. When shaft rotation is not present, a liquid tight seal is maintained at the static sealing interface between the static sealing lip 10 and the mating counter-surface 11 of the seat, and between the dynamic sealing lip 12 and the counter-surface 14 of the shaft.
When shaft rotation takes place, the hydrodynamic seal remains stationary with respect to the housing, and maintains a static sealing interface with said housing, while the seal-to-shaft interface becomes a dynamic sealing interface. The inner peripheral surface of the hydrodynamic seal inner lip 12 incorporates a geometry that promotes long seal life by hydrodynamically lubricating the dynamic seal-to-shaft interfacial zone, and by excluding environmental contaminates from the seal to shaft interface. The inner peripheral hydrodynamic seal lip 12 incorporates a wavy, axially varying edge 15 on its lubricant side, and a straight, sharp edge 16 on its environmental side. The radial cross-section of FIGS. 2 and 2A is taken at a circumferential location which represents the average width of the dynamic sealing lip. As relative rotation of the shaft takes place, the wavy, axially varying edge 15 on the lubricant side of the dynamic sealing lip, which has a gradually converging relationship with the shaft in the axial and circumferential directions, generates a hydrodynamic wedging action that introduces a lubricant film between the seal inner surface 13 and the counter-surface 14 of the shaft per the teachings of U.S. Pat. No. 4,610,319. This lubricant film physically separates the seal and the shaft, and thereby prevents the typical dry rubbing type wear associated with conventional non-hydrodynamic squeeze packing type seals, and thereby prolongs seal and mating shaft surface life and makes higher service pressures practical. This hydrodynamic action, which is described in detail in U.S. Pat. No. 4,610,319, can more easily be understood by referring to FIG. 3, which shows a flat development of the cylindrical sealing surface 14 of the shaft, and which depicts the footprint of the dynamic inner lip 12 of the seal against the sealing surface 14 of the shaft. From an orientation standpoint, the lubricant is shown at 6, the seal footprint is shown at 17, and the environment is shown at 7. The lubricant side of the footprint has a wavy edge 18 created by the wavy edge 15 of the seal, and the mud side of the footprint has a straight edge 19 created by the sharp circular corner 16 of the seal. The lubricant is pumped into the dynamic sealing interface by the normal component V.sub.N of the rotational velocity V.
Referring again to FIG. 2 and FIG. 2A, the sharp circular corner 16 of the environmental side of the seal is not axially varying, and does not generate a hydrodynamic wedging action with the environment in response to relative rotary motion, and thereby functions to exclude particulate contaminants from the seal-to-shaft interface per the teachings of U.S. Pat. No. 4,610,319. Slight axial shaft motions occur in many types of rotating machinery due to component flexibility and various internal clearances. The sharp corner 16, which is commonly known as the exclusion side or exclusion edge, excludes contaminants by performing a shaft scraping function during such axial shaft motions. Thus, as relative axial movement occurs between the shaft and seal, accumulated contaminants are scraped from the sealing surface of the shaft so that the dynamic sealing interface remains free of contaminants. This exclusionary action is described in detail in U.S. Pat. No. 4,610,319.
The illustration of FIGS. 2 and 2A illustrates the customary type of general purpose Kalsi Seals rotary shaft seal that positions and configures the exclusionary edge 16 and the environmental end 9 of the seal 5 in such a manner that they are largely supported by the gland wall 20 in a manner that resists distortion and extrusion of seal material in those instances when the seal is subjected to the hydrostatic force resulting from the lubricant pressure acting over the area between the static sealing interface and the dynamic sealing interface. Such force occurs when the lubricant pressure is higher than the environment pressure. FIGS. 1, 2 and 2A show the seal being forced against the gland wall 20 by hydrostatic force resulting from the lubricant pressure acting over the area between the static sealing interface and the dynamic sealing interface.
The projection 21 of the static sealing lip is typically less than or equal to one-half of the nominal radial compression so that most or all of the seal surface from circular corner 23 to circular corner 24 is brought into close proximity or direct contact with the mating counter-surface 11 of the seating groove when the seal is compressed. The close proximity and/or contact between the seal and the seat groove in the general vicinity of circular corner 23 provides stability against clockwise twisting of the seal within the gland, with the clockwise direction being visualized with respect to FIG. 2. This seal stabilization feature is important in implementations where a hydrostatic and/or mechanical force is applied to the environmental end 9 of the seal, such as during transient pressure fluctuations or when the dynamic sealing interface exclusionary edge 16 is required to actively scrape contaminants off of an axially moving shaft. The projection 22 of the dynamic sealing lip 12 is substantially greater than one-half of the nominal radial compression of the seal so that the seal surface at the radially inner circular corner 25 is not brought into contact with the relatively rotating counter-surface 14, and so that the angulated, axially varying hydrodynamic inlet geometry 15 is not overly flattened against the relatively rotating counter-surface so that the intended hydrodynamic wedging of lubricant into the dynamic sealing interface is not impeded by any undesirable gross distortion of the hydrodynamic geometry.
The static sealing lip 10 has generally the same cross-sectional geometry as the average cross-sectional configuration of the dynamic sealing lip 12 except that it is shorter; therefore when the seal is compressed, the interfacial contact force profiles and deformation of the two lips are very similar in both magnitude and location, and as a result, there is no gross tendency for the seal to twist within the gland. This means that the abrupt sharp edge 16 remains compressed firmly against the shaft, and can perform its intended scraping and exclusionary function so that contaminants from the environment do not enter the dynamic sealing interface.